1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) panel and a fabrication method thereof, and more particularly, to an LCD panel with a hybrid ball spacer structure and a fabrication method thereof.
2. Description of the Prior Art
Due to the continued development in LCD technology, LCD devices have been applied to all kinds of information products, such as personal computers, personal digital assistants (PDAs), mobile phones, or other portable information products. Furthermore, the LCD devices even have gradually replaced the traditional display devices of cathode ray tube (CRT). The main elements of an LCD device includes the LCD panel, which comprises two transparent substrates and a liquid crystal layer disposed between the transparent substrates, while sealant and spacers are used for holding the cell gap between the transparent substrates. Currently, one drop fill (ODF) process is a common liquid crystal filling process, wherein the liquid crystal margin of the LCD panel directly influences the yield of the ODF process. If the liquid crystal margin is too small, the yield of the ODF process will be too low to mass-produce LCD panels. Generally, one of the main factors influencing the liquid crystal margin includes the pattern design of the spacers between the transparent substrates. Taking the conventional photo spacers as an example, they are formed through a single photolithography process, and all the photo spacers have the same height or thickness. However, the flexibility of the materials of conventional photo spacer is poor. Therefore, when a pattern of high spacer-density is designed for the photo spacers, the LCD panel will have a good local pressure resistance but a bad flexibility, which influences the process tolerance window. In contrary, if the photo spacers have a low spacer-density pattern, the LCD panel will have a better flexibility but a weak local pressure resistance.
In order to improve the above-mentioned disadvantages, the manufacturers have developed hybrid photo spacers arranged between the transparent substrates. Hybrid photo spacer structure means the photo spacers have different heights. Referring to FIG. 1, FIG. 1 is a sectional view of a conventional LCD panel. The conventional LCD panel 10 has two transparent substrates 12 and 14, a liquid crystal layer 16 and a plurality of photo spacers 18a and 18b. Since the height of the photo spacers 18a is larger than the height of the photo spacers 18b, the liquid crystal margin can be improved. However, the fabrication of the photo spacers 18a and 18b with different heights needs at least two photolithography processes, which needs much process time and costs.
With reference to FIG. 2, FIG. 2 is a schematic diagram of the sectional view of another conventional LCD panel. The LCD panel 20 includes two transparent substrates 22 and 24, a liquid crystal layer 26, and a plurality of photo spacers 28, wherein all the photo spacers 28 have the same height. However, in order to provide the functionality similar to the photo spacers 18a and 18b with different heights of the LCD panel 10 in FIG. 1, the LCD panel 20 further includes a metal matrix layer 30 disposed between some of the photo spacers 28 and the transparent substrate 22 for increasing the liquid crystal margin. Although only one photolithography process for forming the photo spacers 28 of the LCD panel 20 is needed, at least an extra process is still required for forming the metal matrix layer 30. As a result, the LCD panel 20 still has the disadvantage that the fabrication process is too complex.
In addition, the conventional photo spacers have another disadvantage that the material cost is high. Therefore, how to fabricate spacers with various heights between the transparent substrates through simple fabrication process and low cost in order to improve the liquid crystal margin is still an important issue of the manufacturers of LCD panel.